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Optical Illusions, or Visual Illusions, are images that are deceptive or misleading and they take advantage of the brain's ability to interpret data. Some illusions make you question what you are seeing, while others make you stop and think, and a select few just make your brain give up!

These illusions are split into two types: Physiological Illusions mess with your mind, and Cognitive Illusions make your brain work hard trying to figure out what is going on.

Physiological Illusions

Let's have some fun first. These illusions are all static images, there is no animation and the image does not change. What you see when you look at these illusions is what your brain ends up interpreting. These illusions take advantage of certain defects of the eyes and brains ability, so what you see isn't real.

The first illusion is my personal favourite. Stare at the dot in the centre of the image, and move your head towards the screen, and back again.

Revolving Circle Illusion

Revolving Circle Illusion

The Internet

This is not a trick, there is no animation, you really did see the two circles moving.

The next illusion is a more famous example. Try and look at the dark blobs between the lines.

Grid Illusion

Grid Illusion

The Internet

Its difficult isn't it? That's because there are NO dark blobs. This illusion takes advantage of the "blind spot" at the back of our eyes (optic nerve) where our brains fill in the missing data based on what it thinks should be there.

This next illusion may make you question what you are seeing; all the lines are perfectly straight and parallel. All the boxes are the same size.

Sakuras Illusion

Sakuras Illusion

The Internet

The McCollough effect

The McCollough effect

The Internet

The McCollough effect, named after American psychologist Celeste McCollough, has sparked hundreds of academic papers but there appears to be no concrete evidence of what causes it.

Now for the last physiological illusion: Believe it or not, both numbered squares are exactly the same shade of grey.

Grey Square Optical Illusion

Grey Square Optical Illusion

Edward H. Adelson

No really, they are. I had to use Photoshop to compare the colours, A and B are both the same shade, however, the illusion is created by the shadow of the cylinder, and of the checked pattern.

Cognitive Illusions

Typically Cognitive Illusions create the impression of two opposite ideas, both valid, but not at the same time, the most famous of which is the duck or rabbit image.

Duck Rabbit

Duck Rabbit

Wikipedia

The brain sees one image, but not the other, until it is pointed out. You can then switch between the two. Other Cognitive Illusions include the gradient optical illusion where the inner gradient is actually a solid, unchanging colour:

Gradient optical illusion

Gradient optical illusion

And the famously confusing trick that makes the two halves of your brain conflict. Try it, it's harder than you think!

Brain Conflict

Brain Conflict

The Internet

The final illusion is a great trick sent to me via email. Try it yourself and be amazed at how your eyes can be deceived (there is animation in this one).

If your eyes follow the movement of the rotating pink dot, the dots will remain only one colour, pink.

If your brain works normally this is neat.

If your brain works normally this is neat.

The Internet

However, if you stare at the black " + " in the centre, the moving dot turns to green.

Now, concentrate on the black " + " in the centre of the picture. After a short period, all the pink dots will slowly disappear, and you will only see only a single green dot rotating.

It's amazing how our brain works. There really is no green dot, and the pink ones really don't disappear. This should be proof enough; we don't always see what we think we see.

And one more last illusion (no really, this is the last one!) Read this paragraph out loud:

Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

Now, LOOK at the words.  ;) 

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